Abstract:
Circadian clocks are thought to confer adaptive advantage to organisms by appropriately scheduling behaviours in accordance with environmental conditions, and it is this feature of the clock (Ψ, phase of entrainment) that is under the purview of natural selection (Vaze and Sharma, 2013). Laboratory selection on different phases of behaviour and subsequent examination of the correlated responses of various clock properties is therefore likely to reveal genetic correlations between such clock properties and the phasing of rhythmic behaviours, and the manner in which they do so. This we think will enable us to understand the manner in which circadian clocks evolve to serve their adaptive functions. In this regard we initiated a long-term laboratory selection experiment wherein flies from four large, outbred populations of Drosophila melanogaster were selected for morning and evening emergence (Kumar et al., 2007). Along with a direct response in terms of increased emergence during morning and evening hours in the ‘early’ and ‘late’ populations respectively, correlated responses in many other clock properties were observed. The period (τ) of the ‘early’ and ‘late’ populations were shorter and longer than the ‘control’ populations respectively for both the activity-rest and eclosion rhythms, and the phase-shift responses to light pulses for eclosion rhythm among the populations were also different (Kumar et al., 2007), and later studies showed that other clock properties such as zeitgeber (cyclic environmental signal, such as light-dark cycles) sensitivity over prolonged durations, oscillator amplitude, and inter-oscillator coupling were different in these populations as a result of selection on delayed Ψ of emergence (Vaze et al., 2012a; Nikhil et al., 2016a).
